Frost collector evaporator coil



May 7, 1968 M. W. STEELMAN FROST COLLECTOR EVAPORATOR COIL Filed Oct.27. 1966 FIG. 6

39 INVENTOR MELVIN w. STEELMAN m c 9 ATTORNEY United States Patent3,381,494 FROST COLLECTOR EVAPORATOR COIL Melvin W. Steelman, Niles,Mich., assignor to Clark Equipment Company, a corporation of MichiganFiled Oct. 27, 1966, Ser. No. 589,980 7 Claims. (Cl. 62-283) ABSTRACT OFTHE DISCLOSURE A refrigerated case has ductwork for carrying cool airthrough evaporator coils by drawing the air through a channel. Withinthe channel, a primary cooling coil is located downstream from asecondary cooling coil that removes most of the moisture from the airbefore the air reaches the primary coil. The secondary coil hasindividual vertical fins each in contact with several tubes in avertical line but with only one in a horizontal line. The fins incontact with subsequent sets of tubes in a vertical line are staggeredto obtain several leading edges. The ductwork and secondary cooling coilare constructed to provide a bypass air path around the secondary coilto carry the cooling air upon closing of the secondary coil by anaccumulation of frost.

The present invention relates to a refrigerated case structure, and moreparticularly, to such a structure employing a novel finned refrigeratingcoil construction and arrangement.

Refrigerated cabinets and cases, particularly of the type employed insuper markets and other retail stores, common-ly employ refrigeratingcoils by which air is cooled in movement thereover, circulated throughthe case to cool the products contained therein, and then returned asthrough a duct or passage to pass again over the coil. A plurality ofcoils are usually necessary, arranged one behind or downstream from theother in the air duct or passage. Moisture from the cooling air iscondensed and frozen on the coil as a deposit offrost, which reduces theefficiency of the refrigerating coil, and must be removed from time totime as the accumulation increases. This is normally accomplished bysupplying heat to melt the frost. It is desirable to keep the number offrequency of these defrosts to a minimum. As a practical matter,minimization of defrosting requires reduction in fro-st deposition. Manyattempts have been made to solve this problem, none of them completelysuccessful.

The solution provided by the present invention involves the use of asecondary cooling coil which is disposed in the air passage upstreamfrom one or more primary refrigerating coils, and which is specificallyconstructed for accumulating a great volume of frost thereon. Thesecondary coil is located in the pas-sage to have most of the air flowthereover or there-through and cause deposition of moisture therefrombefore it passes, in a relatively dehumidified condition, to the primaryrefrigerating coils, so that only relatively light frosting of suchother coils occurs. The secondary cooling coil has such construction andspaced relation to the interior of the passage or duct that air maycontinue to flow around or past it to the primary coils, even afterfrost deposition on the secondary coil has reached its maximum, so thatrefrigeration continues with high efiiciency. Heavier frosting of theprimary refrigerating coils then takes place since the air reachingthese coils is not dried by the secondary coil. Frosting of the primarycoils, when it increases to an undesired extent, causes defrosting ofall of the coils in the case by means of known devices for this purpose.The invention increases the capacity of the refrigeration system toaccumulate frost without too great a loss of 3,381,494 Patented May 7,1968 efficiency of refrigerating capacity, and thus increases the lengthof the periods during which refrigeration continues without interruptionfor defrosting to improve the operating efliciency. The invention, asevident, also provides a novel method of controlling frosting inrefrigerated cases.

Objects of the invention are the provision of a refrigerated casestructure by which frequency of defrosting is greatly reduced, of acooling coil structure having great frost-collecting capacity, and of anovel method of extending the intervals between defrosting operations ina refrigerated case or the like.

Other and further objects, advantages and features of the invention willbe apparent to those skilled in the art from the following description,taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical cross-sectional view of the lower portion of arefrigerated case embodying the present invention;

FIG. 2 is a fragmentary plan view of a cooling coil employed in the caseof FIG. 1;

FIG. 3 is a vertical sectional view of the coil, taken substantially asindicated by the line 33 in FIG. 2;

FIG. 4 is a cross-sectional view of the coil, taken substantially asindicated by the line 4-4 in FIG. 2;

FIG. 5 is a fragmentary longitudinal sectional view through the casetaken as indicated by the line 5-5 in FIG. 1, and showing a portion ofthe coil in front elevation; and

FIG. 6 is a fragmentary front elevational view of primary refrigeratingcoils, taken as indicated by the line 6-6 in FIG. 1.

Referring to the drawing, there is shown in FIG. 1 a refrigerated case,generally designated 10, comprising thermally insulated front and rearwalls 11 and 12 connected by an insulated bottom 13, these walls andbottom extending between end walls, one of which is shown at 14 in FIG.5, also of thermally insulated construction. The case body provided bythe walls and bottom may be supported in any suitable manner on a base15.

Within the case body there is provided a well or product compartmentextending between the end walls 14 of the case 10 defined by a frontpanel 16, a rear panel 17, and a bottom panel 18, of a suitable sheetmaterial or the like. The front panel 16, bottom 18 and rear panel 17are spaced respectively from the front Wall 11, bottom 13 and rear wall12 of the case to define a duct or passage generally indicated as 19.Air may be circulated through this duct by means of a fan or blower 20driven by electric motor 21 and suitably mounted in an opening in a fanpanel 22 extending across the air duct or passage 19. The fan 20 drawsair through a preferably screened inlet aperture 23, defined between theupper edge-s of the front wall 11 and front panel '16, to passdownwardly in a forward vertical portion of the duct, under the bottompanel 18 of the product compartment, and upwardly in the rear portion ofthe duct defined between the rear panel 17 and rear wall 12. From therear duct portion, the air is discharged through any suitable outletstructure for cooling of the product compartment and its contents,returning through the inlet aperture 23 to the duct 19 forrecirculation.

In the portion of the passage or duct 19 forwardly or upstream of thefan 20, there is provided a refrigerantevaporating coil generallydesignated 25, which may be referred to as a secondary or cooling coil,or frost-collecting coil, to distinguish from primary or refrigeratingcoils hereinafter mentioned. The coil 25 comprises a suitable number ofpipe or tube portions 26 in two groups or series each consisting of apair of sets, the particular construction illustrated employing fourtube portions in each set, the four tube portions of each set beingdisposed in substantially the same vertical plane. The tube portions 26in each set of each group or series are offset vertically from those inthe other set of that group, as is clearly evident from FIGS. 1, and 3to inclusive. Header plates 27, which may have oppositely directed upperand lower flanges, mount the tube portions. Return bends 28 at oppositeends of the coil each connect a tube portion of one set with a tubeportion of the other set of a group, providing a continuous flow pathfor a fluid refrigerant through each of the two groups of tube portions26 and bends 28. A tube portion at one end of each group has a suitableconnection to a refrigerant inlet line or conduit 29 common to the twogroups, and a tube portion of each group at the end opposite the tubeportion connected to the inlet conduit 29 has a suitable connection to acommon refrigerant return line 30.

The refrigerant, in accordance with commercial practice, is suppliedunder pressure from a suitable source through the inlet conduit 29, andis returned through line 30 after expansion and evaporation in the coil25 to effect cooling thereof. The refrigerant is then compressed andcondensed by any well-known means, not shown, to be again supplied tothe coil as desired. In the present case, the tube portions extendhorizontally in a direction transverse of the air path, with adjacentsets of tube portions spaced apart in the direction of air flow.

A plurality of fins 31 are secured on the tube portions 26 of each set,the fins being relatively narrow and elongated as best evident fromFIGS. 3 and 4. An appreciable space is provided between the fins of theseveral sets in the direction of air flow. As best shown in FIGS. 2 and5, the fins 31 of one set are offset laterally, or longitudinally of thetube portions, from the fins of the adjacent set. The fins of alternatesets are also offset vertically relative to each other, as is best shownin FIGS. 4 and 5. At one or more points along the length of the coil 25,plates 32, which may be flanged at their upper and lower ends andpreferably of the same width as the fins, but of greater height orlength, are secured on the four sets of tube portions in the same planetransverse of the coil. These plates replace fins 31 on two of the setsand are interposed between fins of the other two sets. Tie elements 33,shown as angle members, are bolted or otherwise secured to the upper andlower ends of the plates 32. This construction, best shown in FIGS. 2, 3and 5, assures that the tube portions will be maintained in the desiredspaced and offset relation throughout their length, and rigidifies thecoil assembly.

The secondary or cooling coil 25 is so dimensioned and located relativeto the interior of the duct or passage 19, specifically the horizontalportion thereof below the bottom panel 18 of the product compartment, asto leave a space or spaces through which air may flow about or around,rather than through or over, the coil. In the present instance, the coilis mounted in the duct so as to be spaced from at least one of the endwalls 14, as shown in FIG. 5. As frost builds up on the coil 25, ittends to block passage of air through the coil, and may accumulate in asulficient volume to present a substantially solid barrier to air flow.The coil 25 may be mounted in the duct or passage 19 in any suitablemanner, as by securement of the bottom flanges of the headers 27 and thelower tie elements 33 to the bottom 13 of the case by any appropriatemeans. Upper flanges of the headers and the upper tie elements 33 may bedisposed in supporting relation to the bottom panel 18 of the productcompartment, if desired, as shown in FIGS. 1 and 5.

On the leading or upstream side of the coil 25, there are suitablymounted a plurality of vertical brackets 34 which support elements of anelectrical resistance heater 35 in the form of one or more wires or rodsextending horizontally along the cooling coil 25. The heater 35 is of aknown construction, and is connected to a suitable source of electricityfor activation in a predetermined manner.

In the vertical rear portion of the duct or passage 19,

downstream from the secondary or cooling coil 25 and fan 20, there isprovided at least one primary or refrigerating coil 36, two such coilsappearing in FIG. 1, suitably supported for flow therethrough of airwhich has been drawn through the inlet 23 by the fan 20. Therefrigerating-coils 36 are of conventional construction, comprising tubeelements 37 supported on headers 38, and carrying fins 39 common to allthe tube elements and spaced longitudinally therealong. Therefrigerating coil or coils 36 may provide the greater portion of therefrigerating capacity of the case 10, the cooling coil 25, providingthe balance. Defrosting of the coils is controlled in accordance withthe frosting of the primary coils 36, by means of any of several knowndevices for this purpose, although in the alternative, defrosting may beinitiated by time mechanism set in accordance with knowledge of thenumber of defrosts required during a given period of time, correspondingto a given frost accumulation, based upon trial and/or experience. Thecoils 36 may be supplied with refrigerant from the same source as thecoil 25.

The refrigerating coil structure has preferably each coil successivelydownstream from the first 0r farthest upstream refrigerating coil 36provided with a fin spacing less than that of the preceding orimmediately upstream coil, as shown in FIG. 6. Thus if the farthestupstream coil 36 has a fin spacing of the next coil downstream mighthave its fins spaced /2" apart, the third /3, and so on within practicallimits. Because the air becomes progressively drier as it passes throughthe successive coils 36, it deposits less and less frost on the coils asit moves over them. The progressively closer spacing of the fins allowsmore fins to be used, improving refrigerating efficiency by affordingmaximum heat transfer surface area for the coils within a given space,but bridging or clogging of the fins and coils by frost is notaccelerated.

In coil 25, the fins 32 of each set are equally spaced from each otheralong the tube portions 26 by a distance considerably greater than thespacing of the fins 39 of the refrigerating coils 36, as for exampledouble that spacing. Fewer fins are employed, reducing the refrigeratingcapacity of the coil 25, since its heat transfer surface area is lessthan otherwise, but the secondary coil 25 is primarily afrost-collecting or dehumidifying coil and not a refrigerating coil. Theprimary or refrigerating coils 36 are relied upon for the major portionof the refrigerating capacity of the case, as already mentioned. In aspecific embodiment, the spacing of the fins 32 of the coil 25 is 1 /2"as compared to for the fins 39 of that refrigerating coil 36 disposedfarthest upstream.

The wide spacing of the fins of the secondary coil 25 provides foraccumulation of a heavy frost deposit thereon without bridging the spacebetween the fins. The laterally offset arrangement of the fins of oneset relative to those of the adjacent set, and the provision ofrelatively narrow fins so that each fin is in contacting relation withonly one set of tube portions rather than being common to all of thetube portions of the coil, affords a maximum number of leading fin edgesfor presentation to the air flowing therepast. Frost builds up somewhatin a teardrop or streamlined formation on fins of refrigerating coils,there being a greater accumulation on and adjacent the leading orupstream edge than at the trailing edge, so that it is advantageous toprovide as many fins as possible without close spacing thereof. Thespacing apart of the fins on the several sets of tube portions in thedirection of the air flow, so that the rear or downstream edges of eachset of fins are spaced forwardly of the forward or upstream edges of theset of fins behind or downstream thereof, allows a buildup of frost onthe leading fin edges without bridging thereof to the trailing edges ofthe forward fins, particularly since the alternate sets of fins arelaterally offset. The vertical offsetting of the sets of fins furtherincreases the volume of frost which may be deposited on the coil 25,since the fins of two of the sets have portions projecting above thelevel of those of the other set, so that the air may impinge directlythereon without interference by or contact with other fins. The upwardlyprojecting fin portions also have a maximum of space to accumulate frostthereon. Thus a maximum accumulation of frost on these projecting finportions may be effected. A similar result is achieved by the lowerportions of the fins of the other set, as will be evident. The verticaloffsetting of the tube portions of alternate sets effects changing ofdirection of the air, for increased contact and hence greater moisturedeposition.

The spacing of the secondary coil from the interior surface of duct 19assures that the air will be properly circulated in the volume and atthe velocity required to maintain the case and its contents at thedesired temperature for a period additional to that required to effectthe maximum frost buildup on the coil. This additional period dependsupon the time required for the air flowing through the primary orrefrigerating coils 36, not substantially dehumidified by the coil 25,to provide such accumulation or deposit of frost on the primary coils asto diminish fiow or circulation of air to a point which would notmaintain the refrigerating temperature. At or before this point,defrosting is effected in any of a number of known ways, by closing of acircuit or circuits through the heater 35, so that the air circulatedthrough the case is warmed and melts the frost from the coils 25 and 36.Upon termination of the defrosting operation, the refrigeratingoperation is resumed.

The secondary or cooling coil 25, disposed in the path of cooling airupstream of the primary or refrigerating coils 36, is constructed tocollect frost and thus retard 0r largely prevent frost deposition on theprimary coils. At the same time, it is so dimensioned and arranged inthe air duct that air may pass thereabout in the event it becomesblocked or clogged by frost, so as to maintain refrigeration. By alsoproviding for defrosting in accordance with the frost condition of theprimary refrigerating coils, the number and frequency of defrostsrequired to maintain the case in eficient refrigerating condition isgreatly reduced. The condition and appearance of the product in the caseare never adversely affected. In addition, economy of operation isachieved over what would otherwise be possible.

It will be evident that the invention, in addition to the novelstructure, provides a novel method for controlling frosting ofrefrigerated cases and the like, and more specifically of lessening thefrequency of defrost or lengthening the intervals between defrosts.

The embodiment of this inventive concept illustrated herein is exemplaryand not exhausive, the invention not being limited thereto sincemodifications and variations thereof may be made through a wide rangewithout departing from the spirit and scope of the invention as setforth in the appended claims.

I claim:

1. A refrigeration structure having a primary refrigerating coil in aduct for flow of cooling air and a secondary finned cooling coilupstream of said primary refrigerating coil,

said secondary coil comprising a plurality of generally parallel tubeportions extending generally normal to the direction of air flow andarranged in sets extending generally in a plane normal to the direc tionof air flow with said sets spaced apart along the direction of coolingair flow, and a plurality of groups of spaced apart relatively narrowelongated fins arranged generally parallel to the direction of air flow,with each group of fins respectively secured on the tube portions ofeach set in heat-conducting relation, with said fins of each grouphaving each fin connected only to tubes: of one set, with said finsoffset laterally relative to the fins of each adjacent set, with eachgroup of fins spaced apart from each other along said flow direction,and with said lateral fin spacing of each group of said secondary coilbeing considerably greater than that of said primary coil; and

said secondary coil dimensioned and located relative to said duct toprovide passage for a continuing flow of air to the primaryrefrigerating means in the event of impedance of air fiow through thesecondary coil as by frost accumulation thereon.

2. A structure as defined in claim 1 in which said secondary coil finspacing is greater than that of the fins of the primary refrigeratingmeans by a multiple of the order of two.

3. A structure as defined in claim 1 in which the fins of adjacent setsare offset from each other in a direction substantially normal to saidair flow direction and to said direction of lateral offset.

4. A structure as defined in claim 1 in which the tube portions ofadjacent sets are offset from each other in a direction substantiallynormal to said air flow direction and said direction of lateral offset.

5. A structure as defined in claim 1 in which said primary refrigeratingmeans comprises a plurality of finned refrigerating elements arrangedone substantially directly downstream of another with the fins extendinggenerally in said direction of air flow.

6. A structure as defined in claim 5 in which the spacing of the fins ofthe farthest upstream of said refrigerating elements is greater thanthat of at. least one of the elements downstream thereof.

7. A structure as defined in claim 5 in which the spacing of the fins ofat least some of said refrigerating elements is progressively smaller inthe downstream direction.

References Cited UNITED STATES PATENTS 2,929,229 3/1960 Detwiler 62-4263,091,942 6/1963 Dickson et a1. 62--80 3,099,914 8/1963 De Witt et al.62-283 X 3,199,581 8/1965 Kritzer -151 X 3,209,553 10/1965 Sohda 622833,267,692 8/1966 Pfeiffer et a1. 62-272 X 3,333,437 8/1967 Brennan62-256- ROBERT A. OLEARY, Primary Examiner. W. E. WAYNER, AssistantExaminer.

